1. Field of the Invention
The present invention relates to field electron emission sources having carbon nanotubes and methods for manufacturing the same.
2. Discussion of Related Art
Field emission displays (FEDs) are a relatively new and rapidly developing flat panel display technology. Compared to conventional technologies, e.g., cathode-ray tube (CRT) and liquid crystal display (LCD) technologies, field emission displays are superior in having a wider viewing angle, lower energy consumption, a smaller size, and a higher quality display. A field electron emission source is an essential component in FEDs and has been widely investigated in recent years.
Carbon nanotubes (CNTs) are very small tube-shaped structures, essentially having a composition of a graphite sheet rolled into a tube. CNTs produced by arc discharge between graphite rods were discovered and reported in an article by Sumio Iijima entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). CNTs have extremely high electrical conductivity, very small diameters (much less than 100 nanometers), large aspect ratios (i.e. length/diameter ratios greater than 1000), and a tip-surface area near the theoretical limit (the smaller the tip-surface area, the more concentrated the electric field and the greater the field enhancement factor). Thus, CNTs can transmit an extremely high electrical current and have a very low turn-on electric field (approximately 2 volts/micron) for emitting electrons. In summary, CNTs are among the most favorable candidates for electron emission terminals of a field electron emission source, and can play an important role in FED applications.
A conventional method for manufacturing the field electron emission source utilizes a screen-printing process. In this method, a CNT paste having CNTs and conductive paste is formed on a cathode and then calcined to form a CNT composite layer. Most CNTs embedded in the CNT composite layer cannot emit electrons. For this reason, a surface of the CNT composite layer is cut and polished to form electron emission portions. However, in this mechanical method, the formation of the electron emission portions cannot be accurately controlled. Further, the field electron emission source has a low field electron emission efficiency due to a shielding effect caused by closer, adjacent CNTs.
Therefore an accurately controlled method for manufacturing field electron emission sources and a field electron emission source with high field electron emission efficiency are desired to overcome the above-described problems.